In this Project 2, we propose to study mouse neurons in order to better define in a model system the neuronal and synaptic phenotypes induced by high-risk schizophrenia (SCZ) mutations, to test whether the mouse phenotypes concur with those observed in human neurons (cross-platform validation), and to explore the relation of such phenotypes to SCZ-associated symptoms in human patients, experiments that can only be performed in mice but not in humans. Thus, this project is an essential component for the pursuit of the overarching goals of this application, which are to determine whether different high-risk mutations for SCZ produce a synaptic phenotype, where such phenotypes exhibit commonalities, and whether future screens for therapeutics to ameliorate such phenotypes can be developed. Inherent in these goals is the need not only to validate the reproducibility of phenotypes across platforms, but also to relate such phenotypes to symptoms observed in SCZ. Project 2 will focus in mouse neurons on the same mutations that constitute the focus of the studies on human neurons in the other projects, namely the Nrxn1 heterozygous and homozygous deletions, the minimal critical 22q11.2 deletion, and the 16p11.2 duplications and deletions. The three specific aims of this project will be carried out in a collaborative fashion coordinated by Stanford University (Tom S?dhof and Marius Wernig), with contributions by Rutgers University (Zhiping Pang), the U. of Cincinnatti (Bruce Aronow), and Eli Lilly (John Isaac). These three specific aims are: (1) To determine the neuronal and synaptic phenotypes of primary medial prefrontal cortex neurons that carry Nrxn1 gene deletions, the minimal critical 22q11.2 deletion, or the 16p11.2 duplication or deletion, (2) to test whether iN cells produced from mouse embryonic fibroblasts (MEFs) and iPS cells derived from mutant mice replicate the phenotype of the respective mutations in primary neurons, and (3) to determine the effects of the Nrxn1 gene deletions, the minimal critical 22q11.2 deletion, and the 16p11.2 duplication on synaptic properties of neurons in situ in brain slices of the medial prefrontal cortex. Together, the three specific aims will utilize an interdisciplinary approach to study SCZ pathophysiology in mouse models of the disorder, and provide vertically and horizontally integrated cross- validations of the effects of SCZ-associated high-risk mutations on neuronal function in mice. They will enable not only validation of the results obtained with human iN cells in Projects 1 and 3, but also facilitate a translation of such results into a conceptual framework for understanding SCZ-associated behavioral changes.